Plasma processing systems are used in the manufacture and processing of semiconductors, integrated circuits, displays, and other devices or materials. Plasma processing can be used to transfer a pattern of an integrated circuit from a lithographic mask to a semiconductor substrate. The lithographic mask can comprise an etch-resistant photoresist layer that is deposited over a substrate, exposed to a selected lithographic pattern and developed. In addition to the photoresist layer, the lithographic mask structure can include additional mask layers, e.g., anti-reflective coatings (ARCs). ARC layers are frequently used to reduce light reflections from the substrate during lithography steps, and sacrificial masks can be used to pattern areas on a substrate. The substrate is then anisotropically etched in a plasma process where the patterned photoresist/mask layers define openings in the substrate.
The minimum feature sizes of microelectronic devices are approaching the deep sub-micron regime to meet the demand for faster, lower power microprocessors and digital circuits. A critical dimension (CD) of a circuit is the width of a line or space that has been identified as critical to the device being fabricated to operate properly and it further determines the device performance.
The minimum initial feature size that can be achieved using a layer of photoresist material is limited by the lithographic techniques used to expose and pattern the photoresist layer. Commonly, a dimension of a patterned photoresist (PR) layer is trimmed beyond the limits of the lithographic technique utilizing plasma etching methods. The reduction in CD during the plasma etching process is referred to as CD-bias. However, a consequence of plasma PR-trim process is iso-dense CD-bias, which is the difference between the CDs of dense (closely spaced) and isolated structures, while keeping all other processing parameters (e.g., focus and exposure) constant. This is due to the nature of the neutral-dominant isotropic etching process.